1. Field of the Invention
The invention relates to a device for the display of color images and can be applied to a projection screen type device as well to a direct vision type device. The invention relates particularly to means used to improve the luminous efficiency and, at the same time, the resolution of the color image in display devices using a single light spatial modulator screen.
2. Description of the Prior Art
A light spatial modulator screen generally comprises an array of elementary modulation cells, each corresponding to an elementary surface of the image to be formed. The screens, the modulation cells of which are of the type using a birefringence effect such as liquid crystal cells for example, generally modulate only one component of polarization of light, in such a way that the working of an image display device using a spatial modulator of light such as this requires the selection of one of the two orthogonal directions of polarization of light. The result of this is that the complementary direction of polarization is not used.
Furthermore, to make a color image with a liquid crystal display (LCD) screen type of spatial modulator screen, the liquid crystal cells are most commonly organized into chromatic triplets R-G-B. Each triplet has a cell assigned to the red, a second cell assigned to the green and a third cell assigned to the blue. This assignments are achieved by means of colored filters mounted so as to face each cell.
This organization of the LCD screen into chromatic triplets results in a major loss of transparency, and hence of light, because each component of light is absorbed by colored filters on two-thirds of the surface of the modulator screen. This loss of light gets added to the loss caused by the fact that one of the directions of polarization is not used.
Furthermore, the resolution of a color image thus formed is only one third of the resolution of a monochromatic image that would be obtained with the same LCD screen.